As commonly known, a mold split insert is used in a complementary pair thereof for molding portions (e.g. threads, lugs, rings, and other laterally projecting features) of a molded article that would otherwise be entrapped therein. In particular, a portion of the molding surface is split, usually in half, between the complementary pair of split inserts, and wherein a step of de-molding the molded article is accomplished by separating the complementary split inserts.
Without specific limitation, it is known to use split inserts in a molding stack assembly for the production of injection molded preform of the type that are subsequently blow molded into plastic bottles. In such a stack assembly, the split inserts are commonly known as neck ring inserts because of their role in forming a neck portion of the molded article.
A typical injection mold for the production of plastic preforms includes one or more molding cavities. Each molding cavity is generally configured within a stack assembly of mold inserts. In the injection mold the stack assembly is typically arranged in a mold shoe that includes a set of water cooled plates and a hot runner. The hot runner distributes a flow of injected plastic melt that is received from an injection unit of a molding machine into the molding cavities.
With reference to FIG. 1, a section along a portion of an injection mold 1 illustrates a typical molding insert stack assembly 50 that is arranged within a mold shoe. The molding insert stack assembly 50 includes a neck ring insert pair 52, a mold cavity insert 54, a gate insert 56, a locking ring 58, and a core insert 60, that are configured to cooperate in providing a molding cavity 61 along a set of molding surfaces disposed thereon. The mold shoe includes a cavity plate 62, a core plate 64, a stripper plate 66, and a slide pair 68. Of course, there are many other styles of injection molding insert stack assemblies 50. For instance, it is not unusual to configure the molding insert stack assembly 50 without a locking ring, and wherein the core insert is configured to include the features of the locking ring.
In more detail, the cavity insert 54 is arranged within a complementarily configured bore within the cavity plate 62, while the gate insert 56 is arranged within a bore configured in a top portion of the cavity insert 54. The cavity plate 62 includes coolant channels 72, 74 for connecting coolant channels 55, 57 configured around the cavity and gate inserts 54, 56 with a coolant source and sink (not shown). As can be seen, a substantial portion of an outside surface of the molding cavity 61, corresponding to a body and an end portion of the preform, is provided along the molding surface portions 90, 92 disposed on the cavity and gate inserts 54, 56, respectively.
Similarly, the core insert 60 is arranged on a front surface of the core plate 64, and is retained thereon by the locking ring 58. The core plate 64 also includes coolant channels 76, 77, 78 for connecting a coolant channel configured within the core insert 60 with the coolant source and sink (not shown). The core coolant channel is provided between an inside surface of a bore that is configured along a substantial length of the core insert 60 and a core cooling tube 80 that is arranged therein. Alternatively, a flow partition may be used to divide the core coolant channel into interconnected channels as described in U.S. Pat. No. 4,571,171 to Blank et al. granted on Feb. 18, 1986. As can be seen, the inside surface of the molding cavity 61, corresponding to an inside surface of the preform, is provided along the molding surface portion 91 disposed along the core insert 60. Likewise, the top surface of the molding cavity 61, corresponding to a top portion of the preform, is provided along the molding surface portion 94 disposed on the locking ring 58.
Arranged between the cavity and core inserts 54, 60 is the neck ring insert pair 52. As can be seen, the remaining portion of the outside surface of the molding cavity 61, corresponding to a neck portion of the preform, is provided along the molding surface portion 96 disposed along the inside surfaces of the neck ring insert pair 52. The neck ring insert pair 52 includes a pair of complementary neck ring inserts that are mounted on adjacent slides of the slide pair 68. The slide pair 68 is slidably mounted on a top surface of the stripper plate 66. The stripper plate 66 is arranged on the top surface of the core plate 64, and includes apertures for the locking ring and core inserts 58, 60. As commonly known, and as, for example, generally described in commonly assigned U.S. Pat. No. 6,799,962 to Mai et al, granted on Oct. 5, 2004, the stripper plate 66 is configured to be extensible relative to the core plate 61, when the mold in arranged in an open configuration, whereby the slide pair 68, and the complementary neck ring inserts mounted thereon, can be laterally driven, via a cam arrangement (not shown), for the release of the molded preform from the molding cavity 61. The slide pair 68 also includes an inlet and an outlet coolant channel 70 (only one of which is shown) for connecting a coolant channel 17 configured within each neck ring insert with the coolant source and sink (not shown).
The typical neck ring insert has a body that includes a pair of projecting portions 4 that extend from a top and a bottom face of a generally rectangular flange portion 5. An outer portion of the projecting portions are typically configured as a male taper for cooperating with a complementary female taper on the adjacent cavity, locking ring or core inserts 54, 58, 60 for aligning the neck ring insert pair therewith. Of course, other means are commonly known for aligning the neck ring inserts with the adjacent inserts, such as transposing the male and female tapers of adjacent inserts, the use of taper locks and the like. The flange and projecting portions are typically configured on an integral body composed of a hard durable material such as a tool steel, or a stainless steel.
The neck ring coolant channels 17 are typically formed (e.g. drilling) in the flange portion 5 of each neck ring insert in a simple configuration that includes two intersecting cylindrical channels in a central portion thereof. The foregoing cooling arrangement provides for a cooling of the flange portion 5 which in turns cools the projecting portion 4 and the molding surface disposed thereon through conduction.
However, with increasingly aggressive molding cycles, and the resultant reductions in mold cooling time, a temperature gradient may be imparted around the molding surface that can be a source of certain defects in the molded preform. In particular, an effect of the inhomogeneous cooling can manifest as a localized ‘sink mark’ (i.e. small depressions) in a relatively thick-walled preform feature (e.g. preform support ledge 98, or pilfer proof band 99) in angular positions that are in proximity to a mating interface between the neck ring inserts where the cooling is at a minimum (i.e. the molding surface is at a maximum distance to the coolant channel 17).
Alternatives to the aforementioned neck ring cooling configuration are provided with reference to U.S. Pat. No. 5,599,567 ('567) to Gellert granted on Feb. 4, 1997, or to United States Pat. RE38,396 ('396) to Gellert granted Jan. 27, 2004. In particular, these references describe neck ring inserts that include a coolant channel configuration that includes an effective channel that extends peripherally around a molding surface portion.
The '567 patent describes a neck ring half with an enclosed coolant channel configuration that includes a curved inner channel that extends around a curved inner molding surface disposed thereon. While the reference is completely silent as to a means by which to construct the neck ring insert pair, it is clear that the formation of the coolant channel configuration therein would preclude the use of conventional metal machining methods.
The '396 patent describes a method of making a neck ring insert that includes the steps of forming a inner cylindrical part, which fits in an outer flange part, wherein the inner part is made by casting rather than conventional machining methods. The inner part has a generally cylindrical outer surface with grooves therein to partially form inner portions of two coolant channels. Each coolant channel extends around the curved inner surface of one of the neck ring inserts. The outer flange part includes an opening therethrough having an inner surface which fits around the outer surface of the inner cylindrical part and having respective inlets and outlets configured therein extending to the coolant channels. The outer flange part and the inner cylindrical parts are formed separately and then brazed together. The integrally joined inner and outer parts are then cut in half along the central longitudinal axis to form the complementary neck ring insert pair.
While the foregoing examples of neck ring inserts include a coolant channel configuration that may mitigate the problem of inhomogeneous cooling around the molding surface, they are also complicated and costly to manufacture. Accordingly, there is a need for a coolant channel configuration for use in split inserts that not only provides for a substantially homogenous cooling of at least a portion of the molding surface disposed thereon but that is also relatively simple and more economical to manufacture.